1. Field of the Invention
The present invention relates to an indicating device used for a paper cassette and for indicating a remaining amount of recording papers supplied to a thermal printer or the like.
2. Description of the Related Art
As to thermal printers, there are a thermal sensitive printer and a heat transfer printer in each of which an exclusive recording paper is used. The recording paper (thermosensitive recording paper) used in the thermal sensitive printer comprises cyan, magenta and yellow thermosensitive coloring layers which are stacked on a support member, such as described in Japanese Patent Laid-Open Publication No. 61-213169. Each coloring layer has dispersed micro capsules in which coloring materials are contained. The respective coloring layers of the thermosensitive recording paper are colored by different heat energy. Thus, the coloring layer may be selectively colored by changing the applied heat energy. After the upper coloring layer has been thermally recorded, this upper layer is fixed, so as not to be colored again, before the lower layer is thermally recorded. Fixing the coloring layer is carried out such that the light having a particular wavelength, for example the ultraviolet ray, is applied to the recorded coloring layer. When the thermosensitive recording paper is exposed to an ordinary light source for a long time, its coloring properties are affected. Thus, the thermosensitive recording paper is contained in a light-shielding envelope, and this envelope is contained in a paper box.
When the printer is loaded with the recording paper, at first, a packing envelope is opened to take the paper package out of the envelope. Then, the recording package is set in a paper cassette. Further, this paper cassette is set in the printer.
In case of confirming an amount of the recording papers remaining in the paper cassette, it is necessary to take the paper package out of the paper cassette for observing it after the paper cassette has been taken out of the printer. This confirming work is troublesome. It is considered that a window for confirming the remaining amount of the recording papers is provided, such as a paper cassette in which an ordinary recording paper is contained. Through this window, the remaining amount of the recording papers may be directly observed. However, the thermosensitive recording paper has photosensitivity so that if the window for confirming the remaining amount is provided, the recording paper is exposed to the light. As a result, coloring properties of the recording paper are changed. Thus, it is not practical to confirm the remaining amount of the recording papers through the window. Moreover, the recording paper is thin so that a changing amount of the remaining amount is small when a change of the remaining amount is merely detected. Due to this, it is difficult to indicate the remaining amount with accuracy.